Composition for liquid crystal color display elements

ABSTRACT

A composition for nematic liquid crystal color display elements, said composition comprising at least one anthraquinonic dye represented by the following formula ##STR1## wherein X and Y are identical or different and represent --NH 2  or --OH; Z represents halogen, --OR, --NHR, ##STR2## --CONHR 2  or --COOR 2 , in which R represents an alkyl group having 1 to 15 carbon atoms or a lower alkyl group optionally substituted by --OH, ##STR3## represents hydrogen, halogen, --OH, --OCH 3 , an alkyl group having 1 to 15 carbon atoms, or a methoxy group optionally substituted by ##STR4## and R 2  is a phenyl group, an alkyl group having 2 to 5 carbon atoms or a cyclohexyl group; and n is an integer of 1 or 2 provided that when X is --NH 2  and Y is --OH, and when X and Y are both --OH, n is an integer of 1, and when n represents an integer of 2, the two Z&#39;s may be identical or different dissolved in at least one nematic liquid crystal.

This invention relates to a composition for liquid crystal color display elements utilizing an electro-optical effect, comprising nematic liquid crystals and a dichroic dye. More specifically, this invention relates to a composition for nematic liquid crystal color display elements used in display devices utilizing the electro-optical effect of nematic liquid crystals, said composition comprising at least one nematic liquid crystal and at least one dichroic anthraquinonic dye dissolved therein, said dye being represented by the following formula ##STR5## wherein X and Y are identical or different and represent --NH₂ or --OH; Z represents halogen, --OR, --NHR, ##STR6## --CONHR₂ or --COOR₂, in which R represents an alkyl group having 1 to 15 carbon atoms or a lower alkyl group optionally substituted by --OH, ##STR7## R₁ represents hydrogen, halogen, --OH, --OCH₃, an alkyl group having 1 to 15 carbon atoms, or a methoxy group optionally substituted by ##STR8## and R₂ is a phenyl group, an alkyl group having 2 to 5 carbon atoms or a cyclohexyl group; and n is an integer of 1 or 2 provided that when X is --NH₂ and Y is --OH, and when X and Y are both --OH, n is an integer of 1, and when n represents an integer of 2, the two Z's may be identical or different,

preferably at least one dichroic anthraquinonic dye of the formula ##STR9## wherein R₃ represents a linear or branched alkyl group having 2 to 15 carbon atoms.

Liquid crystal display devices containing dichroic dyes having already been known as "guest-host" mode display devices in the field of liquid crystal technology, and are utilized as display devices in watches, portable electronics calculators, televisions, etc.

The theory of this type of display device is that dichroic dye molecules are aligned according to the alignment of the molecules of a liquid crystalline material. Specifically, the liquid crystal molecules change from an "off" state to an "on" state and are oriented upon the application of an external stimulation which is normally an electric field, and incident to this, dichroic dye molecules are simultaneously oriented. As a result, the degrees of absorption of light by the dye molecules in the two states change to achieve a color display.

Such an electro-optical effect means a liquid crystal color display utilizing the so-called guest-host effect. The guest-host mode is presently operated by a method which involves the use of nematic liquid crystals having positive or negative dielectric anisotropy and a method which involves the use of liquid crystals that show phase transition from a cholesteric phase to a nematic phase upon the application of an electric field.

Some dichroic dyes which operate in accordance with this theory have been known heretofore, but none of them have proved to be entirely satisfactory in their performance in commercial applications. This has partly hampered the development and commercialization of liquid crystal color display devices based on this theory.

Dichroic dyes used in liquid crystal color display devices based on this theory must meet certain basic requirements. For example, they are generally required to have a sufficient coloring ability in small amounts, a high dichroic ratio that enables them to show a high contrast by application of voltage or absence of voltage, sufficient solubility in liquid crystals, excellent durability and high stability. Additionally, they should not deteriorate the performance of the device even when used for a long period of time.

The present invention provides anthraquinonic dyes of formula (I) or (II) as dichroic dyes which meet these requirements.

Typical examples of these dichroic anthraquinonic dyes are shown in Tables 1 and 2 below.

                  TABLE 1                                                          ______________________________________                                                                      Color in                                          Dye                          chloroform                                        No.  Structural formula      solution                                          ______________________________________                                               ##STR10##              Red                                               2                                                                                    ##STR11##              Red                                               3                                                                                    ##STR12##              Red                                               4                                                                                    ##STR13##              Red                                               5                                                                                    ##STR14##              Red                                               6                                                                                    ##STR15##              Reddish violet                                    7                                                                                    ##STR16##              Reddish violet                                    8                                                                                    ##STR17##              Reddish violet                                    9                                                                                    ##STR18##              Reddish violet                                    10                                                                                   ##STR19##              Violet                                            11                                                                                   ##STR20##              Violet                                            12                                                                                   ##STR21##              Violet                                            13                                                                                   ##STR22##              Orange yellow                                     14                                                                                   ##STR23##              Orange yellow                                     15                                                                                   ##STR24##              Orange yellow                                     16                                                                                   ##STR25##              Orange yellow                                     17                                                                                   ##STR26##              Orange yellow                                     18                                                                                   ##STR27##              Red                                               19                                                                                   ##STR28##              Red                                               20                                                                                   ##STR29##              Red                                               21                                                                                   ##STR30##              Red                                               22                                                                                   ##STR31##              Red                                               23                                                                                   ##STR32##              Red                                               24                                                                                   ##STR33##              Red                                               25                                                                                   ##STR34##              Red                                               ______________________________________                                    

                                      TABLE 2                                      __________________________________________________________________________                               Change in color                                                                by alignment                                                                          Upon                                                                    Absence                                                                               application                                   Dye                       of electric                                                                           of electric                                   No.                                                                               Structural formula     field  field                                         __________________________________________________________________________     26                                                                                 ##STR35##             Red    Colorless                                     27                                                                                 ##STR36##             Red    Colorless                                     28                                                                                 ##STR37##             Red    Colorless                                     29                                                                                 ##STR38##             Red    Colorless                                     30                                                                                 ##STR39##             Red    Colorless                                     31                                                                                 ##STR40##             Violet Colorless                                     32                                                                                 ##STR41##             Bluish violet                                                                         Colorless                                     33                                                                                 ##STR42##             Bluish violet                                                                         Colorless                                     34                                                                                 ##STR43##             Blue   Colorless                                     35                                                                                 ##STR44##             Blue   Colorless                                     36                                                                                 ##STR45##             Blue   Colorless                                     37                                                                                 ##STR46##             Blue   Colorless                                     38                                                                                 ##STR47##             Blue   Colorless                                     __________________________________________________________________________

The dichroic dyes in accordance with this invention can be synthesized from known materials in accordance with known reactions. Since the resulting crude dyes frequently contain inorganic salts and other impurities, they have to be purified by extraction or recrystallization with organic solvents, preferably by thin-layer chromatography or column chromatography.

The following Synthetic Examples show the preparation of typical dichroic dyes in accordance with this invention.

SYNTHETIC EXAMPLE 1

Synthesis of a compound identified as Dye No. 1 in Table 1:

Potassium hydroxide (2.5 g) was added to 30 g of phenol, and dissolved at 100° C. Then, 9 g of 1-amino-2-bromo-4-hydroxyanthraquinone was added and reacted at 160° C. for 4 hours. The resulting reaction mixture was cooled, and a dilute aqueous solution of sodium hydroxide was added. The mixture was stirred, and filtered. The filtration cake was washed with water and dried to afford 8.0 g of a crude dye. Recrystallization from ethanol afforded a compound identified as Dye No. 1 in Table 1. This product was a red dye which showed a maximum absorption at a wavelength of 515 mμ.

Compounds identified as Dyes Nos. 2 to 7 in Table 1 can be similarly synthesized by using the corresponding phenols or anilines instead of the phenol in the above procedure.

SYNTHETIC EXAMPLE 2

Synthesis of compounds identified as Dyes Nos. 13 to 17 in Table 1:

Compounds identified as Dyes Nos. 13 to 17 were synthesized in the same way as in Synthetic Example 1 except that 2-bromo-1,4-dihydroxyanthraquinone was used instead of 1-amino-2-bromo-4-hydroxyanthraquinone and reacted with the corresponding phenols.

SYNTHETIC EXAMPLE 3

Synthesis of a compound identified as Dye No. 8 in Table 1:

The captioned compound can be synthesized by operating in the same way as in Synthetic Example 1 using n-octylamine instead of the phenol. It can, however, be advantageously synthesized by the following procedure.

Five grams of the compound identified as Dye No. 5 in Table 1 was reacted with 15 g of n-octylamine at 150° C. for 2 hours. Steam was introduced into the reaction solution to remove the excess of unreacted amine by distillation. The precipitate was separated by filtration, washed with water, and dried to afford 5.5 g of a crude dye. The crude dye was purified by chromatographing it on a column packed with a silica gel powder using chloroform as a developing agent. Thus, a compound identified as Dye No. 8 was obtained. This product was a reddish violet dye which showed a maximum absorption in a chloroform solution at a wavelength of 519 mμ.

A compound identified as Dye No. 9 in Table 1 can be similarly synthesized by using n-dodecylamine instead of n-octylamine.

SYNTHETIC EXAMPLE 4

Synthesis of a compound identified as Dye No. 10 in Table 1:

Ten grams of sodium 1-amino-4-(p-toluenesulfonylamide)-anthraquinone-2-sulfonate was added to a solution of 21 g of potassium hydroxide in 45 g of methanol. The mixture was stirred at 80° C. for 2 hours. Water was added, and the precipitate was separated by filtration, washed with water and dried. Five grams of the methoxylated product so obtained was stirred in 50 g of conc. sulfuric acid at 40° C. for 1 hour, and then discharged onto ice water. The precipitate was separated by filtration, washed with water, and dried to afford 4.4 g of a crude dye. Recrystallization from ethanol afforded a compound (Dye No. 10) as dark violet pillar-like crystals. This product was a violet dye which showed a maximum absorption in a chloroform solution at a wavelength of 529 mμ.

Compounds identified as Dyes Nos. 11 and 12 in Table 1 can be synthesized similarly to the above procedure using phenols instead of methanol. Advantageously, however, these compounds can be synthesized by operating in the same way as in Synthetic Example 1 except that 1,4-diamino-2-bromoanthraquinone is used instead of 1-amino-2-bromo-4-hydroxyanthraquinone and reacted with the corresponding phenols.

SYNTHETIC EXAMPLE 5

Synthesis of a compound identified as Dye No. 18 in Table 1:

5.0 g of 1-amino-4-hydroxy-2-phenoxyanthraquinone, 20 g of octyl alcohol and 1.2 g of potassium carbonate were reacted at 150° C. for 30 hours in a stream of nitrogen. The reaction mixture was cooled, and 50 g of methanol was added. The precipitate was filtered. The filtration cake was washed with methanol and water, and dried to afford 3.5 g of a crude product. The crude product was chromatographed on a column of silica gel using benzene as an eluent. Thus, 0.4 g of 1-amino-4-hydroxy-2-octoxyanthraquinone (Dye No. 18) was obtained. This product was a red dye which had a melting point of 130° to 132° C. and showed a maximum absorption in chloroform at a wavelength of 513 mμ and 550 mμ.

Other dichroic dyes which may be used in this invention can be synthesized substantially in accordance with the above Synthetic Examples.

The present invention is further described with reference to the drawings.

FIG. 1 is a front elevation of a liquid crystal display device incorporating the composition of this invention; and

FIG. 2 is a cross-sectional view taken along the line a--a of FIG. 1.

Referring to the drawings, a nematic liquid crystalline substance colored with a dye is filled in a layer 1 interposed between two parallel-laid glass slides 2 and 3. The glass slides 2 and 3 are spaced from each other by spacers 4 defining both side ends of the layer 1. The slides 2 and 3 respectively have on their inner surfaces transparent electrodes 5 and 6. The electrode 5 is connected to an external lead wire 9 through a contact 7. Likewise, the electrode 6 is connected to an exterior lead wire 10 through a contact 8. The electrodes 5 and 6 are of rectangular shape and are disposed face-to-face to each other. A voltage source 12 and a switch 11 connected thereto in series are connected between the exterior lead wires 9 and 10. The voltage source 12 supplies a dc voltage or an ac voltage of low frequency sufficient to re-orient the liquid crystal molecules and dichroic dye molecules in the layer 1 and align them on the inner surfaces of the slides 2 and 3. Usually, voltages of 10 to 20 V are sufficient.

An example of the nematic liquid crystal used in this invention is a mixture composed of 43% of 4-cyano-4'-n-pentyl biphenyl, 17% of 4-cyano-4'-n-propoxy biphenyl, 13% of 4-cyano-4'-n-pentoxy biphenyl, 17% of 4-cyano-4'-n-octoxy biphenyl, and 10% of 4-cyano-4'-n-pentyl terphenyl. There can also be used a so-called chiral nematic liquid crystal mixture obtained by adding 5% of cholesteryl nonanoate, 3% of optically active 4-cyano-4'-isopentyl biphenyl, etc. to the aforesaid mixture. This chiral nematic liquid crystal mixture is in the cholesteric phase in the absence of electric voltage, but phase transition to the nematic phase occurs upon the application of voltage. The above examples are not limitative, and other liquid crystalline compounds which have a nematic liquid crystalline phase showing positive or negative dielectric anisotropy can be used either singly or as mixtures in this invention.

The dichroic dyes in accordance with this invention are used either singly or as mixtures. The concentration of the dichroic dye in the liquid crystalline substance is such that the dye dissolves in the liquid crystals, and the dye molecules can be fully oriented and aligned by the orientation of the liquid crystal molecules. Generally, the suitable concentration of the dye is 0.01 to 20% by weight, preferably 0.01 to 3% by weight, based on the liquid crystalline substance. It is also possible to obtain the desired color hue by mixing the dichroic dye in accordance with this invention with another dichroic or non-dichroic dye or colorant.

In the making of such a liquid crystal display device, transparent electrodes are treated in advance so that the liquid crystal molecules and the dichroic dye molecules may be oriented parallel or perpendicular to the surfaces of transparent electrodes. The treatment can be performed, for example, by a method comprising simply rubbing the surfaces of the transparent electrodes with a cotton cloth, etc. in a fixed direction, a method comprising coating a silane-type compound, a method comprising vapor deposition of silicone oxide, or a method comprising coating a silane-type compound or depositing a vapor of silicone oxide, and then rubbing the surfaces of the transparent electrodes with a cotton cloth, etc. in a fixed direction.

When a solution consisting of nematic liquid crystals having positive dielectric anisotropy and the dichroic dye in accordance with this invention is filled in a liquid crystal color display device which has been treated so that the liquid crystals and dye molecules may be oriented parallel to the surfaces of transparent electrodes, the display device is of the type wherein the color of the electrode portions disappears upon the application of voltage.

When a solution consisting of nematic liquid crystals having negative dielectric anisotropy and the dichroic dye in accordance with this invention is filled in a liquid color display device which has been treated so that the liquid crystal and dye molecules may be oriented perpendicular to the surfaces of transparent electrodes, the display device is of the type wherein the electrode portions are colored upon the application of voltage.

The display devices shown in FIGS. 1 and 2 are of the type which permits viewing of transmitted light. These devices may become reflective-type display devices if the glass slide 2 is replaced by a non-transparent reflecting plate, or by placing a reflective plate rearwardly of the slide 2 to permit viewing from ahead of the glass slide 3.

There are a diversity of liquid crystals and methods available in making liquid crystal color display devices using the dichroic dyes in accordance with this invention. Essentially, all of them can be classified as displaying methods based on a guest-host mode utilizing the electro-optical effect of nematic liquid crystals.

The following typical Examples illustrate the present invention specifically. The invention, however, is not limited to these Examples. All percentages in these Examples are by weight.

EXAMPLE 1

In a display device of the type shown in FIGS. 1 and 2, Silicone KF-99 (a trademark of Shin-etsu Chemical Co., Ltd. for a silicone compound) was coated on the surfaces of transparent electrodes 5 and 6. The layer 1 of this display element was filled with a colored liquid crystal solution composed of 0.1 part by weight of Dye No. 1 shown in Table 1 and 9.9 parts by weight of a liquid crystal mixture consisting of 38% of 4-cyano-4'-n-pentyl biphenyl, 8% of 4-cyano-4'-n-pentoxy biphenyl, 23% of 4-cyano-4'-n-heptyl biphenyl, 8% of 4-cyano-4'-n-heptoxy biphenyl, 10% of 4-cyano-4'-n-octoxy biphenyl, 10% of 4-cyano-4'-n-pentyl terphenyl and 3% of optically active 4-cyano-4'-isopentyl biphenyl. A plastic film having a thickness of 10 μm was used as spacer 4.

When the switch 11 was opened, this display device was seen to be colored distinctly red. When the switch 11 was closed and an ac voltage of 20 V at 60 Hz was applied, that portion of the device at which the transparent electrodes 5 and 6 faced each other became almost colorless. When the switch 11 was opened, the device again showed a red colored state. When the display device was placed in the light path of a spectrophotometer, the maximum absorption wavelength was 524 mμ. When the switch 11 was opened and closed at this wavelength, the ratio of absorbance was 1:6 showing good dichroism.

When this display device was subjected to irradiation of visible light having a wavelength of more than 400 mμ for a long period of time, no change was noted in color hue, the ratio of absorbance, etc., and the display device retained the same properties as it had immediately after construction.

EXAMPLE 2

When Dye No. 8 shown in Table 1 was used instead of the dye used in Example 1, a display of violet color and colorlessness was obtained by the opening and closing of the switch 11.

EXAMPLE 3

When Dye No. 15 shown in Table 1 was used instead of the dye in Example 1, a display of orange yellow color and colorlessness was obtained by the opening and closing of the switch 11.

EXAMPLE 4

When Dye No. 22 shown in Table 1 was used instead of the dye in Example 1, a display of red color and colorlessness was obtained by the opening and closing of the switch 11. 

What we claim is:
 1. A composition for nematic liquid crystal color display elements, said composition comprising at least one nematic liquid crystal and at least one anthraquinonic dye represented by the following formula ##STR48## wherein X and Y are identical or different and represent --NH₂ or --OH; Z is bonded to the 2-position and/or 3-position relative to X and represents --OR, --NHR, ##STR49## --CONHR₂ or --COOR₂, in which R represents an alkyl group having 4 to 15 carbon atoms or a lower alkyl group substituted by --OH, ##STR50## R₁ represents hydrogen, halogen, --OH, --OCH₃, an alkyl group having 1 to 15 carbon atoms, or a methoxy group optionally substituted by ##STR51## and R₂ is a phenyl group, an alkyl group having 2 to 5 carbon atoms or a cyclohexyl group; and n is an integer of 1 or 2 provided that when X is --NH₂ and Y is --OH, and when X and Y are both --OH, n is an integer of 1, and when n represents an integer of 2, the two Z's may be identical or different, or one may be the group defined above and the other may be a halogen, said anthraquinonic dye being dissolved in the nematic liquid crystal.
 2. The composition of claim 1 wherein said anthraquinonic dye is represented by the following formula ##STR52## wherein R₃ represents a linear or branched alkyl group having 4 to 15 carbon atoms.
 3. The composition of claim 1 or 2 wherein a mixture of said anthraquinonic dyes is dissolved in at least one nematic liquid crystal.
 4. The composition of claim 1 or 2 wherein a mixture of said anthraquinonic dyes is dissolved in a mixture of nematic liquid crystals.
 5. The composition of claim 1 or 2 wherein the concentration of said anthraquinonic dye is 0.01 to 20 percent by weight based upon the weight of the nematic liquid crystal.
 6. The composition of claim 5 wherein said concentration is 0.01 to 3 percent by weight based on the weight of the nematic liquid crystal.
 7. The composition of claim 1 or 2 wherein said nematic liquid crystal has a positive dielectric anisotropy.
 8. The composition of claim 1 or 2 wherein said nematic liquid crystal has a negative dielectric anisotropy. 